The overall objectives of this project are to understand the endocrinology of the human glycoprotein hormones, thyroid-stimulating hormone (TSH), choriogonadotropin (hCG), luteinizing hormone (LH), and follicle-stimulating hormone (FSH), and thereby to develop diagnostic and therapeutic clinical applications. Recent research progress includes the following: delineation of the biological relevance of low and high affinity TSH binding sites in human thyroid membranes and elucidation of the role of the carbohydrate moiety of hCG in its thyrotropic activity. Future investigations will evaluate the role of the galactose-terminated glycoprotein pathway in the metabolism of fully glycosylated proteins, explore the nature and biological relevance of hCG alpha-subunit heterogeneity in pregnancy, and develop clinical applications for ultrasensitive glycoprotein hormone assays.